OOPS!! Just realized upon close inspection, the grime is actually old lacquer and the beautiful brass I see is where it has worn off. How do I clean these up or do I have to take to a professional metal shop?

Buy some BRASSO-it may be hard to find, but ask anyone that has been in the ARMY and they will tell you the same thing. I would take the knobs off and dab a little brasso on an old rag and start with a small circuling motion, you will be shocked at the black grime on the rag. When you are done they will look like new! Brasso works well on copper ,Gold and silver too. I cleaned up an 1864 Indian head penny and it looks new. Brasso is what we used in the military to clean and polish our brass buttons.
Hubert
huberthn@windstream.net